Reed switches are electromechanical switches having two reed blades formed of a conductive ferromagnetic material, typically a ferrous nickel alloy. In the presence of a magnetic field the overlapping reed blades attract, causing the blades to bend towards each other and make contact, closing an electrical circuit. The two reed blades are positioned within a glass capsule hermetically sealing the reed blades. The capsule typically contains a vacuum, air, or nitrogen at atmospheric or super atmospheric pressure. Reed switches can switch significant power, for example in the range of 10 to 100 Watts. Reed switches also have a long life measured in millions to over 100 million operations without failure or significant increase in contact resistance. Over many cycles the reed contacts can become worn, pitted, or eroded, due to mechanical wear or the electrical arcing as the switch opens and closes. This pitting or corrosion results in an increase in electrical resistance across the closed switch. To prevent, or at least minimize, such erosion the contact surfaces of the reed blades are coated with ruthenium, a hard, high melting temperature metal with relatively low resistivity. Recently the cost of ruthenium has dramatically increased. Known reed switch contact coatings include, for example, a gold layer overlain by a layer of ruthenium, or a layer of titanium of 50-65 micro inches thickness overlain by a layer of ruthenium of 20-35 micro inches, a layer of molybdenum overlain by a layer of ruthenium or a layer of copper 34 micro inches overlain by a layer of ruthenium of 50 micro inches.
What is needed is a reed switch contact arrangement which minimizes the amount of ruthenium or other platinum group metal on the contact faces without decreasing reed switch life.